This invention relates to remote monitoring of fluids for the presence of selected chemical species and, more particularly, to methods and apparatus for in situ monitoring of gases and liquids in ground water and in the vadose zone and liquid chemical waste storage tanks.
Many of the commercial and industrial activities throughout this country produce as by-products large quantities of a diverse variety of chemical wastes, including organic chemicals and radionuclides. It is known that many such chemicals are hazardous to persons and or the environment. It has therefore become increasingly important to test and monitor the environment, including ground water, gases, vadose zone and surface air to determine the presence of, and monitor concentrations of various chemical species. Such monitoring includes the need for monitoring substantial areas by testing at a plurality of thoughtfully positioned test points.
Spectrochemical emission methods have long been used in the laboratory for the detection of elemental and molecular chemical species. Various excitation mechanisms are used in conventional laboratory spectroscopy. These include flame excitation, spark excitation, arc excitation, and inductively coupled excitation. Inductively coupled excitation includes microwave-induced plasma (MIP) and radio-frequency inductively coupled plasma (ICP). For the most part, these analytical methods are embodied in laboratory instruments. Such instruments are physically large and expensive. Consequently, sample analysis is almost always performed in the laboratory.
Laboratory sample analysis is not well suited to environmental monitoring for several reasons. First, samples must be collected in the field and transported to the laboratory for analysis This is a costly and time-consuming procedure. Second, use of these discrete samples is inadequate for close observation of the dynamic ebb and flow of certain characteristics at a site, for example, in ground water. The inability to constantly monitor a site is exacerbated by the delays occasioned in processing discrete samples in overburdened laboratories having limited instrumentation.
Accurate monitoring of a large site requires testing at multiple test points. In doing so, the difficulties and expense of manual, discrete sampling techniques are multiplied. Additionally, it is extremely difficult and cumbersome to collect samples simultaneously from multiple test points by manual techniques.
A technique is known for in situ monitoring of molten metal. U.S. Pat. No. 4,732,477 shows a disposable probe for analyzing samples of molten charges inside the charges themselves. This apparatus is useful only for analysis of a single sample, and cannot be used thereafter, because use of the probe requires solidifying a sample of the molten charge inside a cavity in the probe. The patent shows the use of a light-transmitting body positioned with one end in the cavity of the mold and having a connection to a fiber-optical light conductor extending upwardly through a sample rod to a treating unit such as a spectrometer.
U.S. Pat. No. 4,692,875 shows a metal-alloy indentifier system in which a grinding wheel is used to produce sparks of glowing hot metal Light emitted by the sparks is transmitted via optical cable to a spectrometer for analysis and comparison of the "full spectrum signature" of the metal alloy with similar plots for alloys of known composition, to establish the unknown composition by a positive match with a known alloy.
U.S. Pat. No. 4,666,672 discloses an "optrode" for sensing halogenated hydrocarbons. The apparatus shown in that patent utilizes fluorometric detection of polyhalogenated hydrocarbons. The foregoing patents do not adequately address the problems outlined above.
Accordingly, a need remains for a way to monitor gases and liquids for selected chemical species in situ, in groundwater, the vadose zone and storage tanks.